1. Field of the Invention
The present invention relates to a slip casting method for manufacturing ceramic articles including sanitary wares with traps.
2. Description of the Related Arts
Such a casting process comprises the steps of preparing a slip by dispersing particles of pottery raw materials such as clay in a solvent such as water (referred to simply as "water" hereinafter), casting the slurry into a cavity in porous molds, absorbing the water in the slurry into the porous molds to cause the slip to solidify on the inner surfaces of the molds, and separating the solidified article from the molds. The casting method can be classified into two types: a method called "solid casting" in which water is absorbed from both sides of the cast article into the porous molds, and a method known as "slip draining method" in which water is absorbed from one side of the cast article into the porous mold and any excessive slip is discharged after a predetermined wall thickness of the article has been obtained. The portion formed by the solid casting method is referred to as a solid casting portion, while the portion formed by the slip draining method is referred to as a drain casting portion. In some cases, a cast ceramic article has both solid casting and drain casting portions.
Slip casting is an excellent forming method for the manufacture of ceramic articles in that the articles of complicated configurations can be formed using relatively simple equipment. However, the configuration is undesirably limited due to the fact that the solidification of the slip proceeds substantially uniformly over the entire area of the mold surface. For instance, it is difficult to vary the thickness of the drain casting portion according to position. A solid casting portion is also required to have good balance of thickness over the entire region thereof. Otherwise, the slip in the surrounding portion will solidify before solidification of the slip in the thicknesswise central or core portion, resulting in a defect known as "cavity".
Another factor which limits the configuration of the article to be formed by slip casting is the construction of the mold. In order to realize a complicated configuration, it is necessary that the mold is composed of many core mold parts and/or split mold parts. A too complicated configuration may require that the cast article is partially deformed or broken to allow removal of the core and the split mold parts. Consequently, there is a practical limit to complexity of the mold structure for use in the slip casting process. One measure for casting a ceramic article having a complicated configuration includes the casting of plural components of the ceramic article. The various components are then bonded together using a bonding slurry. This method, however, has many limitations because the bonding itself is a laboratious task and requires a high degree of skill. In addition, more work is required to wipe off any excess bonding slurry forced out from the bonding region. Further, this method may not be applicable depending on the portion of the article, and cracking tends to increase in the proximity of the bonding region during drying and firing.
These restrictions in the configuration and complexity of available molds is a serious problem, particularly in the production of sanitary ware with a trap. In general, the trap included in sanitary wares such as toilet bowls or urinal stalls defines an air tight seal formed by ware to prevent offensive smells or gases from escaping from the sewage pipe. In order to create such a water seal, the outlet piping of the bowl or stall is bent to form a trap.
Conventionally, the main part of such a trap is formed integrally with the body of the bowl or stall and the remainder of the trap is formed separately. The two parts are then bonded together in an extra step to form to the complete trap.
The casting of ceramic article for this purpose has thus encountered restrictions with regard to the thickness and configuration of the article to be cast. It has been impossible to form a ceramic article which does not meet such restriction.
For instance, the design of the trap of a sanitary ware has been largely limited by the configuration of the body of the bowl or stall, because the major part of the trap portion is formed integrally with the body of the bowl or stall. The design of the trap is an important factor which significantly affects the water flushing function of the sanitary ware, so that the design of the sanitary ware is largely restricted by the requirement for water flushing function. Furthermore, this conventional method, which employs the step of bonding the green ceramic body formed separately, essentially requires removal of bonding slip spearing out from the joint surface and tends to allow cracking at the joint during drying and firing.
In order to obviate this problem, Japanese Patent Laid-Open No. 3-272804 discloses a method in which a green ceramic body of most part of a trap is formed separately from the green ceramic body of the bowl or urinal and both green ceramic bodies are bonded together. This method, however, requires a troublesome work for locating both green ceramic bodies correctly relative to each other. In addition, the water flushing function may be impaired by the state of the bond of both green ceramic bodies. Furthermore, bonding itself may fail according to the design of the article.
Accordingly, an object of the present invention is to provide a method of casting a ceramic article, comprising the steps of: preparing a porous casting mold defining a mold cavity; forming separately a green ceramic body; placing the green ceramic body in the mold cavity; and supplying a slip into the mold cavity to form a deposit on the surfaces of the molds, thereby forming the ceramic article composed of the green ceramic body and the deposit of the slip integrated with each other.
According to this method, restrictions on the thickness and configuration of the ceramic article to be cast is reduced to enhance the degree of freedom in the design of the ceramic article.
In another aspect of the present invention, there is provided a method of forming by casting a sanitary ware having a bowl portion and a trap communicating with the bowl portion, comprising the steps of: preparing porous casting mold defining a mold cavity; forming separately a green ceramic body of the trap; placing the green ceramic body in the mold cavity and supplying a slip into the mold cavity; to form a deposit on the surface of the mold, followed by draining, thereby forming the sanitary ware composed of the trap and the deposit of the slip integrated with each other.
This method enables simplification of the forming process and enhances the degree of freedom in the design of the ceramic article. Hitherto, it has been necessary to reconsider the design of the trap each time the design of the sanitary ware is changed, requiring a laborious work for confirming the water flushing performance. Such laborious work can be eliminated by the method of the present invention because a trap which has been tested and confirmed to have sufficient flushing performance can be applied to a variety of models of the sanitary ware products. Consequently, the period for developing a new model has been shortened remarkably.
According to the present invention, the green ceramic body placed beforehand in the mold and the deposit of the slip supplied subsequently are integrated with each other so as not to be separated from each other in the subsequent drying and firing steps. It is therefore preferable that the green ceramic body and the slip have substantially the same composition.
Preferably, the casting is carried out under atmospheric pressure by using a mold made of a self-water-absorbing function such as plaster or, alternatively, pressurizing casting may be adopted in which a pressure-resistant mold such as a resin or ceramics mold is used and water is forcibly migrated into the mold by pressure applied to the slip.
The mold suitably used in the present invention is a composite mold which is composed of a plurality of mold parts which cooperate in defining a mold cavity. The green ceramic body formed in advance has to be held still in this mold cavity. This can be done by suspending the green ceramic body in the mold cavity by using a steel wire or the like which is to be extracted after the separation of the cast article from the mold. Such a method of holding the green ceramic body, however, cannot suitably be applied to the case where the green ceramic body has a complicated construction as is the case of a trap of a sanitary ware or where the green ceramic body is large in size, due to difficulty in correctly locating the green ceramic body. The holding of the green ceramic body in the mold cavity is therefore preferably done by allowing the green ceramic body to rest on a molding surface.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments when the same is read in conjunction with the accompanying drawings.